Internal combustion engines, including diesel-fueled engines, gaseous-fueled engines, and other engines known in the art, exhaust a complex mixture of air pollutants. These air pollutants are composed of gaseous compounds, which include, among other things, the oxides of nitrogen (NOx). Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of NOx emitted to the atmosphere from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine.
It has been established that a turbine engine having a well-distributed flame and low flame temperature can reduce NOx production to levels compliant with current emission regulations. One way to generate a well-distributed flame with a low flame temperature is to use a pre-combustor that vaporizes fuel and heats air for mixture to a predetermined lean fuel-to-air equivalence ratio before injection into a primary combustor. However, pre-combusting requires complex and expensive designs, and the pre-combustion process often excites instabilities that can damage the engine.
One alternative to pre-combusting that has been implemented by engine manufacturers includes injecting the fuel and air into a pre-mixer, along with a flow of hot combustion gases, and then relying on the combustor's internal shape to force the required mixing before ignition occurs. An example of this strategy is described in U.S. Pat. No. 4,351,156 (the '156 patent) issued to White et al. on Sep. 28, 1982. The '156 patent describes a turbine engine having a primary combustion zone, a can-like secondary combustion zone, a dilution zone, and a pre-mixer. Air and fuel are introduced into the pre-mixer in a co-flow relationship, and hot exhaust gases are directed from the primary combustion zone through a bleed port into the pre-mixer. All three fluids then reverse flow directions and enter the primary combustion zone in a direction toward a dome of the zone, where the flow again reverses its direction and flows toward the secondary combustion and dilution zones. This flow reversing is designed to promote complete vaporization of the fuel and uniform mixing of the latter with the air.
Although the turbine engine and combustor arrangement described in the '156 patent may result in low NOx production without a pre-combustor, it may still be complex, costly, bulky, and have suboptimal mixing. In particular, because the combustor arrangement of the '156 patent requires a bleed flow of hot exhaust gases for fuel vaporization, the combustor arrangement is required to have additional passageways to accommodate these flows. The additional passageways increase the number of components, assembly complexity, and cost associated with the turbine engine. In addition, because the pre-mixer is located entirely outside of the combustor and, because the primary combustion zone is axially located relative to the secondary combustion zone, significant space on the turbine engine may be consumed thereby. Further, the flow reversals provided by the combustor arrangement of the '156 patent may be insufficient to optimally mix the fuel and air.
The disclosed combustor and turbine engine are directed to overcoming one or more of the problems set forth above.